This application proposes to measure the increase in essential fatty acid requirement caused by dietary trans fatty acids, to study the effect of double bond position in fatty acids upon their metabolism, and to detect, measure and identify unusual polyunsaturated fatty acids derived from dietary trans fatty acids. The first aim will be approached through study of dose-response studies of dietary linoleate and heart and liver polyunsaturated acids at several constant levels of dietary trans fatty acids. The second aim will involve study of lipase, hydrolysis, acyl exchange and beta-oxidation of isomeric trans-18:1. In the third, the isomeric polyunsaturated fatty acids of tissue derived from trans acids will be isolated, identified and measured.